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There Is No Free Lunch, Episode 763: Lens Adapters

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Lens adapters can be useful things sometimes, letting you mount one brand of lens on another brand of camera.

One thing that has always bothered me, though, is the idea of doubling the number of lens-mount interfaces. When you look at the thick metal pieces on the front of the camera and the back of the lens, and then consider that they have to be lined up exactly parallel to the image sensor, it’s kind of amazing it works.

Although it doesn’t always work. Lloyd Chambers first reported years ago that with high-quality, wide-angle lenses you could detect very small misalignments in the camera-lens mount. Misalignment of 10 microns from side-to-side was enough to cause blur on the sides of the image. Since then a lot of other people have confirmed the same thing.

So when I hear people cavalierly talking about putting an adapter on their camera I tend to cringe. When a single camera-lens interface has enough variability to sometimes be visible, adding another large piece of metal with another mount interface seems a recipe for problems.

Don’t get me wrong. Generally, they’re acceptable or people wouldn’t use them. But I always am curious about what acceptable looks like in the lab.

Optical Bench Testing

We’ve been working a lot with our optical bench, testing large enough quantities of each lens to develop our acceptable ranges, since we plan to start adding this testing to the Imatest testing we currently use for quality assurance. An optical bench isn’t necessarily better than image-based testing programs like Imatest, but it has some specific advantages.

One big difference is that an optical bench tests at infinity (on wide-angle lenses, Imatest or DxOAnalytics may be testing at 4-6 feet focusing distance). Another is it tests the lens directly; the variability of a camera body is eliminated from the loop. There are some things a bench doesn’t do as well, too. For example you don’t get a full picture of the entire lens in one run; you get a line of data from one side to the other. You have to rotate the lens in its mount and do several lines to get a complete picture of the entire lens surface.

Since the information from our optical bench is different from the Imatest graphs I usually use for illustrations, let me go over one quickly.

 

Wells Optical Bench printout of MTF by field of view and frequency.

 

The horizontal axis shows degrees off-center, with “0″ the center of the lens. The vertical axis is the MTF reading (“1″ being theoretical perfection and “0″ being gray mush).

The charted colors show various frequencies. For this graph we chose to show the MTF at 10, 20, 50, and 80 line pairs per mm. Most manufacturers’ MTF graphs limit themselves to 10 and 30 or 10, 20, and 40 as frequencies. We’re including some higher frequencies just because we’re still learning about using this tool to identify bad lenses.

There are two charted lines at each frequency, one representing tangential and the other sagittal lines. When the two lines of the same color are separated, there is some astigmatism. (You don’t have to worry about the terms – just that if the two lines of the same color are widely separated, that’s not good, close together is good.)

The graph above is of a good copy of a good lens, the Zeiss 35mm f/2.0. There are some slight differences away from center with one side having a bit more astigmatism and the other a bit lower MTF at higher frequencies, but this is really minor stuff that wouldn’t show up in photograph.

To give you a bit more experience with this kind of graph, below are printouts from 4 other Zeiss 35mm f/2.0 lenses – all of which are optically excellent as determined by Imatest and careful pixel-peeping.

 

 

Again, let me emphasize that what you’re seeing is normal (actually less than normal) copy-to-copy variation in good copies of the lens. Actual bench testing is almost like fingerprinting. No two copies are exactly the same. Notice the similarities. There is nearly no astigmatism right at the center and similar MTF values, particularly at the 10 and 20 /mm frequencies that are most critical.

To give you some idea of what a not-so-good lens looks like on the same set of parameters, here’s one that’s not so good.

Notice this one is still quite good in the center, but has some major problems developing on the right side. The settings on the optical bench we used for this series make it look much worse than it really is. While the graph makes it look like the MTF drops to zero, that’s simply because the settings we’re using report zero if focusing distance changes greatly or vignetting become severe.  That makes a nice warning signal for ‘some human needs to come check this lens’.

Our parameters are pretty tight: the awful looking graph above actually is a lens that looks a little softer on the right side, but certainly not horrible. An online sized jpg would look perfectly fine, at 50% pixel-peeping or in a large print you’d notice it. I’ll go into more detail about what we can do with the optical bench in some later posts; I just wanted to give you a quick overview for now.

Using Adapters on the Optical Bench

One thing you probably haven’t thought about is that lenses have to be mounted on the bench in order to do these tests. That requires a separate, fairly expensive mount for each brand of lens. Obviously we had to pony up to get mounts for Canon, Nikon, NEX, and Micro 4/3 lenses. But, since I was already pretty unpopular in the accounting department, I hoped to avoid spending a few thousand more dollars to buy Leica, PL, and other mounts for lenses that we have a lower number of copies of.

I knew adapters might cause a problem, but thought, since we carry so many copies of various high-quality adapters, I could certainly find a few that were accurate enough to use. Once again, Roger’s assumptions were way off base. I won’t bore you with dozens and dozens of test results. But I’ll show you a good example. In this case, we took the lens in the upper right of the 4 examples at the top of the page and tested it on a number of Nikon to NEX adapters. Here are 6 examples.

I won’t bore you with another 20 graphs that look pretty much like these. We tried Leica to NEX and Leica to Micro 4/3 adapters, Canon to NEX, etc. We tried different lenses on one adapter. It didn’t really matter. None of them would be acceptable for testing. Not one.

I’ll point out that we carry only name-brand, fairly expensive adapters, not eBay $29 adapters. All of them are tested frequently and used frequently and none of the ones I tested today had any problems. Still, not one of them would be acceptable for testing, so I guess I’m going to have to order those expensive lens mounts after all.

What Does It Mean in the Real World?

Like a lot of laboratory testing, probably not a lot. Adapters couldn’t all stink or people wouldn’t use them. Like a lot of tests, you can detect a very real difference in the lab that doesn’t make much difference at all in the real world.

Videographers are the primary users of adapters, and probably won’t notice the problems at all. Video and cinema cameras shoot at lower resolution (even 4K video) than photography and tend to concentrate on center-frame so they’re unlikely to see a problem.

Even photographers who use adapters are often adapting a larger format lens to a smaller format camera (Leica full-frame lens to Micro 4/3 or APS-C camera, for example). Assuming the lens is higher quality than a native lens they would otherwise be shooting, they might be perfectly happy. Still, I should point out that I  only tested these 35mm lenses out to +/- 12 degrees (their field of view is actually +/- 30 degrees). Even on a Micro 4/3 camera, the lens would have a field of view of +/- 15 degrees what we see here at 12 degrees should be noticeable.

In the examples above, though, center resolution is pretty much unchanged, it’s only when you get away from center that you start to see issues. So someone shooting portraits and centered subjects is unlikely to notice an issue. A landscape photographer, though, would likely see some problems along the edges of the image.

Putting a great lens on your camera via an adapter might still be better than an average native-mount lens. On the other hand, that great lens certainly wouldn’t be as good as it would be on its native-mount camera.

 

Roger Cicala

Lensrentals.com

September, 2013

97 Responses to “There Is No Free Lunch, Episode 763: Lens Adapters”

Otm Shank said:

Hi Roger,

Thank you for the informative post. I have always wanted to see how results from an optical bench test would look like.

Question: Why is the off-center values significantly different between the left and right side on the first plot? It looks like the right side is systematically weaker. Does it indicate that even the native mount is slightly off-center?

Thanks!

James Scholz said:

Once again, great article, Roger. But it makes me wonder if the same problem exists with tel extenders, which introduce additional mount surfaces to the lens-camera equation. Any thoughts on this?

Daemonius said:

What about Leitax? Bit different than usual adapters (I have it on my C/Y 50/1.4 .. works nicely).

eths said:

I use (heavily) two Novoflex adapters for Nikon and Pentax lenses on my Nex7.

I haven’t noticed any negative effects in everyday use. Nonetheless, your test is very interesting, indeed.

Lee Saxon said:

Strange coincidence that all the Zeiss 35/2 copies had a bit more drop in MTF on the right side!

Brian Leighty said:

I have the same question as James but would also through extension tubes in the mix as well since I use those a lot. Great article Roger.

Oskar Ojala said:

I think that very slight deviations from perfect planarity usually don’t matter, since most real world photography isn’t of brick walls. Shooting a landscape at infinity is the tricky proposition that would show issues with planarity. But many native mount lenses also fail that test, reasons including soft corners, field curvature, bad tolerances in manufacturing, inaccuracy of focus and slight misalignment of lens and camera mounts with both still within spec.

Shooting at shorter distances than infinity and more three dimensional subjects, the circumstances themselves tend to mask minor defects and things like overall contrast become more important than a slight tilt of the lens.

Now I’m not saying that this all doesn’t matter, just that real-life performance and value can be a very tricky thing to assess.

LensRentals Employee

Roger Cicala said:

Otm,

We’re trying to figure that out a bit. It’s very consistent with several different mounts.

One thing that has recently been suggested is that the left side of the machine is against a wall, the right side exposed to a very bright room – and the front of the lens is open to that ambient light during testing. I’m going to feel really stupid if turning out the lights makes a difference after running hundreds of tests.

But that seems a likely answer. The mounts we use are rotatable through 360 degrees. If the mounts were tilted I’d expect to be able to see that move over to the left side if we rotated the mount 180 degrees, but we don’t see that at all.

It’s also possible there’s an alignment issue in the bench itself, but repeated checks haven’t revealed it yet.

I’ll also mention that our bench, while giving us some capabilities we really want, is a $50k piece of equipment, which puts it in the ‘economy’ price range (The best ones are 5 times that price). It has 3 separate motors controlling lens rotation, reticle movement, and focusing, which are calibrated to move together. It may be that in this price range we’re going to have a bit of tilt.

Best,

Roger

LensRentals Employee

Roger Cicala said:

DEamonius, I don’t have any Leitax adapters so I can’t comment on them at all.
Roger

CarVac said:

How about less extreme adapters, like Nikon->Canon or Contax->Canon?

They’re usually made out of a single piece of metal, so the variability in a high-quality one should be less than an SLR->mirrorless.

brandon said:

what does Imatest say about the adapters?
Interesting as always Roger, thanks.

Silvio / KH said:

I think you just convinced me not to buy into a NEX system, which I planned to use with my Nikon lenses.

Not sure if I should thank you or not ;)

PenGun said:

I has planed on getting a hold of a Leica Elmar 135 f4 M for my Fuji X-E1. Is the longer focal length going to make an adapted lens less of a compromise. I’m perfectly happy with the Fuji 14mm f2.8 for the short end.

Nqina Dlamini said:

Interesting read as always. I suppose if you had old FD mounts (old Canon) and wanted to use them on EF cameras, you should have some inkling that you are in a compromised situation.
Thanks again. I enjoyed this article (as always).

Don Cox said:

“I think you just convinced me not to buy into a NEX system, which I planned to use with my Nikon lenses.”

I have been using a NEX with Nikon lenses with complete success for the past two years. There are absolutely no problems in practice with normal and longer lenses at normal apertures.

However, I would not use a lens shorter than about 18mm with an adapter at a wide aperture. Depth of focus diminishes with focal length.

Much of my work has been with bellows such as the Nikon PB-4, which has built in “misalignment” in the form of a swing adjustment on the front panel. The depth of focus at the sensor is plenty to cover the inaccuracies of this movement at its zero setting.

Don Cox said:

I would like to see MTF charts for these 35mm lenses (with adapters) at f/4 and f/5.6 as opposed to wide open. My guess is that stopping down a little will increase the depth of focus enough to cover the misalignment.

And who shoots landscapes or cityscapes at f/2 ?

If you are using the lens wide open for one of those shallow depth of field portraits with just one eye in focus, then you can focus that eye correctly wherever it is in the frame. It doesn’t matter if objects in some other part of the frame are focussed at a slightly different distance – usually the aim is to have them out of focus.

If you use the lens wide open for street photography at night, does it really matter if objects on the left side of the picture are in focus a few inches further away than objects on the right side ?

Jose Nuno said:

Adding to the list of reasons to use adapters is also the fact that you can get very interesting lenses for insanely low prices.

I have two manual lenses (52mm f1.8 and 135mm f3.5) that each cost around 30€, and they work fine in a NEX system. Even more so given the fact that the biggest reason for out of focus areas is in my clumsy hastiness focusing manually, and not on the lenses’ tolerances.

I get that you evaluated higher value propositions, and that this setup is not going to work on a pro system where you need better reliability, but I just felt this should be pointed out just the same.

LensRentals Employee

Roger Cicala said:

PneGun,

I’ll run some longer lenses and see. I’m guessing there will be less difference since there’s a narrower angle of view and what we’ve seen has been fine on-center.

LensRentals Employee

Roger Cicala said:

Don, you’re totally correct. 2 stops down generally makes them all look great. Like I said, this stuff is more intellectual exercise, but adapters work pretty well or people wouldn’t use them.

I was looking more from the point of view of “I want to shoot a Canon 35 f/1.4 on my NEX instead of an NEX lens because the Canon is a better lens” (not claiming it is, just that I hear that kind of thing a lot). It may be better in theory than a native mount lens, but not in practice after the adapter is added.

Roger

Lasse Beyer said:

Did you perform any tests with the lights turned out yet? If it makes any difference, you could use some kind of hood to cover the whole thing. Something like the Pelican case where the SigZilla ships in comes to mind here… ;)

Samuel H said:

I have NEX camera, all my lenses are vintage Leitz for the Leica-R mount, I use them with either a cheap adapter from ebay or a Metabones Speedbooster, depending on the situation.
You have to look at the issue as a whole to understand why adapters can be so great: yes, these adapters, specially the cheap one from ebay, must be screwing up the glass-sensor interface; and still, these lenses are incredibly more awesome than anything I could buy today for a similar price. Like, insanely better.
Of course, I should provide proof of what I’m saying, so: sharpness and bokeh tests here:
http://www.similaar.com/foto/lenstests/lenstestsa.html
http://www.similaar.com/foto/lenstests/bokehtests.html

Ben said:

Here’s another vote for running the above combo through Imatest.

Ian Anderson said:

I’ve always wondered about this with people like Marc Adamus shooting the Nikon 14-24 on his Canon bodies with a Novoflex adapter. Obviously it works extremely well for him, but interesting to see the lab results.

Wally said:

I have not used an optical bench tester, but all the optical test systems that I have seen around the laboratory I work at are either set-up with light blocking black curtains or in windowless rooms. A bit of stray light in the lens could certainly lower the image contrast.

NancyP said:

Thanks. I suppose I will see what the real world impact is, given that I just bought a used Nikon 50mm f/1.2 AIS for use on my Canon 6D. Why bother with this lens? Interesting bokeh at f/1.2, at which point there is also some loss of contrast, etc, one of those situations where the lens’ defect can be turned into a feature. It is also said to be very sharp when stopped down.

SteveL said:

You havce probably done this but I wonder if Imatest can see the same difference. Test a lens with and without an adapter on the optical bench then test the same lens with and without the same adapter using Imatest.

LensRentals Employee

Roger Cicala said:

Guys, I’ll try to repeat this with some Imatest measurements, but that’s more time consuming. We can run an optical bench test in about 3 minutes, compared to a 45 minute set up and 15 minutes or so per adapter for Imatest. I need most of my spare time right now to learn my way around the optical bench since we hope to use it for routine lens testing between rentals.

Don Cox said:

Depth of focus was a problem in the days of film, because film (especially 120 size film) does not lie perfectly flat in the image plane. An adapter whose faces are not perfectly parallel has the same effect as film that is not flat – parts of the image will be focussed at a different distance from the rest.

If the subject is at infinity and the lens is wide open, even tiny differences in lens-to-sensor distance can visibly affect focus.

Formulae and tables can be found in the Focal Encyclopedia of Photography. In extreme cases there are figures such as .009mm.

Do we know how accurately the sensors in cameras are placed parallel to the lens mount? What happens if the sensor has 5-axis stabilisation?

Wide aperture lenses with short focal lengths are difficult to make and to use.

Vrecha said:

Reading this article I began to wonder …
Olympus is claiming that 4/3 lenses can be used via their adapter (MMF-3 for example) on their m4/3 bodies. While the newest E-M1 body promises the useful AF performance etc, it would be interested to know how much the image quality is compromised because of the adapter.
It seems to me that you posses the needed knowledge, curiosity and equipment to find the (unbiased) answer.

Samuel H said:

I will add to my previous comment that my tests may not be able to catch tilt issues, since I look at corner sharpness in stills taken focusing at the corner.
I have “focus plane” tests too, where I focus at the center and look at the top-right corner resolution, but that’s just one corner, the results are not posted online, and I must admit I don’t look at them as much as I should.

Peter said:

There are two thing I’m curious about:
* How does this mash with the very nice numbers for the SpeedBooster adapters? Those ought to have the same alignment issues, plus optics?
* How about the Sony LEA1/LEA2 adapters? Those are the transition path from Alpha to E-mount? If my lenses stop working well if I change to E-mount, I’ll be sad.

John M said:

Would the results be the same for a Canon L lens used on the Canon EOS M with the Canon M adapter?

Steinar Knai said:

Roger, thanks for all your good reports, but this one to me lacks substance and your conclusion is totally predictable, even without research. However, since your other reports really are eye-opening, you are excused. Entertaining blog, as always.

LensRentals Employee

Roger Cicala said:

John, I don’t see any reason it wouldn’t be, but we haven’t tested that combination.
Roger

LensRentals Employee

Roger Cicala said:

Steinar, I don’t disagree. But I think, given the number of ‘but what about this combination’ comments, that it served a purpose.

ssam said:

I presume that if your adapter is not perfectly aligned it causes the plane that is in focus to be miss aligned. Similar to using a tilt+shift lens. If you took one of the examples where the resolution drops on one side, and refocused it could you get that side sharp? Is the miss alignment really only a problem if you shoot flat surfaces straight on?

Helene said:

Roger, is it possible for a test on a cheap eBay adapter? It would be a real eye opener if its graph was similar, but not worse, than the expensive adapters.

Bill Layman said:

Roger,

PLEASE do this test on some Olympus MMF-3 (4/3 to micro 4/3) adapters. Many of us are planning to buy several (very expensive) Olympus 4/3 lenses for our new Olympus E-M1 bodies. You could save lots of people a lot of heartache if you showed us the effect of MMF-3 on Super High Quality Olympus lenses.

Fred said:

The real life equivalent of this test is taking a photo of a large painting on the wall at f2 aperture and seeing the edges slightly out of focus. With a live view finder, when a photos of any 3D object is focused on some part of the object within the frame, that part will be exactly in focus. For example, a portrait at f2 of a face in the left or right half of the frame should be fine if focused in composition rather than moving the camera and focusing at the center of frame.

Craig said:

This is very interesting. Still, I have to say that I’ve gotten some of my sharpest digital images using adapters. I went to Yosemite in 2010 and shot mostly with a Canon 5D Mark II using Nikkor F-mount lenses with a Fotodiox adapter. With the best lenses, such as the Nikkor 85mm f/2 AI-S and the Nikkor 28mm f/2 AI, I was getting images that looked amazingly sharp even at 100% view on-screen — even better than I usually got using auto-focus with L-series Canon EF lenses. The corners were less perfect, but still very good; and it’s hard to be sure that the adapter was to blame, since most lenses are better in the center than in the corners. That being the case, while I’m sure your measurements are legit, I have to agree that they probably don’t mean much in the real world. It would be interesting to compare the same lenses on Canon and Nikon full-frame DSLRs of similar resolution; that would show whether the adapter was noticeably worse than the native mount.

What I was hoping for in this article is something I didn’t get, which was an assessment of which brands of adapters tend to be better, and quantifications of the differences. The $29 eBay adapter from Hong Kong probably isn’t as good as a Novoflex or a Fotodiox, but how much worse is it? (Then there’s the OTHER problem with cheap adapters, which is that some of them are very poor mechanically — either the fit is noticeably loose, or the bayonet mount doesn’t lock, or worse, you can’t get the lens off the adapter, or the adapter off the camera…)

Craig said:

Oh, one more thing — unless I missed it, I don’t think you said what f-stop you test at (I would guess you test lenses wide open), nor do you indicate whether stopping down will improve performance (I would think it would, since it will increase depth of focus). The wonderfully sharp pictures I mentioned in my previous comment were mostly shot at f/8 and focused at infinity or the hyperfocal distance, at focal lengths ranging from 20mm to 300mm. Would this have been sufficient to eliminate softness caused by an imperfectly-aligned adapter?

LensRentals Employee

Roger Cicala said:

Craig, that was wide open, and I agree, stopping down would probably eliminate a lot of what we see.
Roger

LensRentals Employee

Roger Cicala said:

Craig, I don’t have any cheap adapter’s to test. We were using mostly Novoflex and Fotodiox adapters in this article.

LensRentals Employee

Roger Cicala said:

ssam – sometimes. It depends on the degree of tilt and if there is also a decentering element. Notice some of the results affect both sides.

David Ruether said:

This article may explain some things I found when adapting many Nikkor (and other) lenses to Panasonic MFT bodies. Oddly, lenses that generally performed well to the full-frame corners at optimum stops when used with film and when shooting infinity-subjects (see: http://www.donferrario.com/ruether/slemn.html) often would not cover sharply the full width of the far smaller digital MFT frame under the same conditions(!). This was true for most lenses shorter than 50mm (such as 20, 24, 28, 28PC, and 35mm), but longer lenses generally performed well everywhere in the MFT frame except when used at the widest stops (where they often performed well on film). Notable exceptions were the Nikkor 16mm *f3.5* fisheye and the 12mm f5.6 Voightlander lenses, both of which performed surprisingly well to the frame corners on MFT when used at f8.5. The Nikon-to-MFT and Leica-screw-to-MFT adapters used were cheap, but performance appeared not to relate to those so much as to the
lenses themselves. Perhaps the quirks involved in using digital sensors with lenses designed in the film era has something to do with the above…?

Stephen said:

It seems to me that the adaptor tests where astigmatism goes to infinity on one side suggest a problem with your testing methodology. Also, do I understand correctly that you are saying that a lens which is soft on the right, when rotated 180 degrees is still soft on the right (that is, the other side of the lens)? If so, it looks like you may have a large enough light infiltration problem that the adaptor results could be showing glare on the inside surfaces of the adaptors.

Kenneth Tanaka said:

Thank you very much for this testing, Roger. It confirms what I thought I had been observing for a long time. Having a substantial inventory of Leica lenses I have naturally attempted to mate them to NEX and Olympus m43 bodies with adapters. Although the most expensive adapter brands did make some difference in image quality it was not significant. Simply put, as only one example, a $7,000+ Leica 24mm Summilux casts a markedly inferior image on a NEX-7 compared to the E-Mount Sony/Zeiss 24mm with 1/7th the price.

So in the end I decided that the inconveniences of adapting these costly lenses to other bodies was simply not worth the effort. The dirty little secret today is, of course, that today’s cameras actively compensate for the optical properties of the lenses they recognize. That, plus autofocus, make native lenses the right choice for today’s advanced cameras.

Morry Korman said:

I wonder how the old Tamron adaptall lens mounts fared in this bench test. There are still many around being used. I have a 17mm SP Tamron that I still use on a Pentax D100. I would rate it as not outstanding but quite good especially at F8 or F11.

LensRentals Employee

Roger Cicala said:

STephen, it’s not infinity. We set up a range of +/- 60 microns of focusing in each direction. It went outside of that, not to infinity.

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